Fig. 1, 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fig. 5. 
Fig. 6. 
PLATE XV. [PLate 26.] 
la. Plerygotus acuminatus. Appendages surrounding the mouth, but little dis- 
turbed (see p. 187). The impressions upon the naturally opposed surfaces of the 
two portions into which the slabis split are both represented. One-half the natural 
size. From Lesmahago. (Museum of Practical Geology.) 
¢, palpi. 
c’, the toothed edges of the endognaths. 
d, the basal joints of the ectognaths ; d’, their serrated processes. 
e, the terminal joints of the ectognathary palp. 
g, the metastoma. 
Plerygotus perornatus. The carapace and appendages (see pp. 187 and 212); natural 
size. From Lesmahago. (Museum of Practical Geology.) 
b, 0’, 6”, 6’, the antenna. 
cc’, endognaths on the right side. 
ce’, endognath on the left side, reversed in position. 
e, terminal joints of ectognathary palp. 
g, the metastoma, displaced. 
x, palps of the endognaths ? 
A problematical fragment ; probably the central lobe of an epistomian plate. Les- 
mahago. (Museum of Practical Geology.) 
Pterygotus ludensis. The penultimate segment and telson, of the natural size; 44., 
the sculpture magnified. Base of Old Red Sandstone, Ludlow Railway. (Mr. 
Lightbody’s cabinet. ) 
Pterygotus arcuatus, The metastoma. Lower Ludlow, Leintwardine. (Museum of 
Practical Geology. ) 
Plerygolus bilobus. A restored diagram, of the natural size. 
a, eyes. 
é, antenne. 4’, the chela. 
c, the endognaths, with their palps. Their basal joints are, for distinctness’ 
sake, represented as if they were widely separated in the middle line. 
d, e, the ectognaths, with their palps. 
Jf, the epistoma or conjoined epistoma and labrum. 
g, the metastoma. 
Ito 13, successive segments; I, carapace; 2-12, segments of the body ; 
13, telson. 
